Headless compression screws are known in the art. U.S. Pat. No. 4,175,555 to Herbert discloses a bone screw with leading and trailing end portions, where the pitch of the uniform single thread at the leading end portion is greater than the pitch of the uniform single thread at the trailing end portion and the end portions are separated by a central unthreaded portion axially longer than either end portion. When the thread of the leading end portion torqueably engages a distal bone fragment while the thread of the trailing end portion torqueably engages a proximal bone fragment and the unthreaded portion spans the fracture, the fragments are longitudinally translated together and subsequentially compressed as a result of the differential in pitch between the leading thread and the trailing thread. Because its unthreaded central portion spans the fracture it is inherent to the Herbert screw that longitudinal translation of the distal bone fragment towards the proximal bone fragment is delayed until the threads of the trailing end of the screw begin engaging the proximal bone fragment; compression occurs once the fragments are in contact and the screw is torqued further.
Several patents to Huebner disclose screws with single threads of continuously varying pitch along its length where, generally, the pitch of the thread at the leading end of the screw is greater than the pitch of the thread at the trailing end. As the screw is torqueably engaged into two bones or bone fragments the differential in pitch of the continuously varying thread causes compression of the bone material along the whole length of the threaded portion of the screw, resulting in simultaneous translation and compression of the separated bones or bone fragments.